Method of determining boric acid in nickel-containing solutions



ll atemrted Aug. l2, W924i.

EDWIN M. BAKER, 0F ANN ARBOR, MICHIGAN, ASSIGNOR TU CHRISTIAN GIRL, OF

, KALAJVIAZOO, MICHIGAN.

METHOD OF DETERMINING BOBIG ACID I1\T NICKEL-GONTAINDTG- SOLUTIONS. I

No Drawing Z '0 all whom it may concern:

- Be it known that I, EDWIN M. BAKER, a citizen of the United States, residing at Ann Arbor, in the county of VVashtenaw and State of Michigan, have invented a certain new and useful Improvement in Methods of Determining Boric Acid in Nickel-Containing Solutions, of which the following is a full, clear, and exact description.

This invention relates to a method of determining the quantity or percentage of boric acid in a nickel-plating solution. In practicing the nickel-plating of various articles, it has been founcl to be desirable, if not necessary, to include a certain proportionofboric acid in the electro-plating solution. For instance, a solution such as has been employed by me with satisfactory results contains, for each gallon of solution 2 ounces of boric acid (11,130,)

32 ounces of nickel sulphate (NiSO,. .7H O).

3.3 ounces of nickel chloride (NiCl,. (ll-LO).

The determination, by titration, of the boric acid content in such nickel-containing solutions has beenpractically impossible with indicators in use heretofore. The presence of the nickel in the solution has resulted in .the precipitation of the nickel before the occurrence of the color-reaction which indicates when the boric acid is neutralized by the standard alkali, with the result that the boric acid content, as indicated, is in excess of that actually present. It has been proposed to remedy this inaccuracy by removing the nickel prior to the addition of the standard alkali; this, however, requires so much time and expense as to render determination by this method impracticable for controlling the composition of commercial nickel plating baths.

By virtue of my invention, I am enabled to determine accurately the boric acid prescut in nickel-containingsolutions without the necessity for precipitating the nickel and, inv fact, irrespective of the presence of nickel therein. 4

" ln practicing my invention, a measured volume or unit ofnickel-p'latiug solution'riis taken. To this isadtlcd a few drops of an acid indicator, known as u'lctlxykoraugc,

Application filed January 24, 1923. Serial No. 614,685.

tion until its color changes to red, or reddish-orange. The purpose of adding the acid is to convert any'borates that may be present into boric acid; and the change in color to red-or reddish-orange occurs when this conversion is completed and without the necessity for the use of an excess of the standard acid, so that the only 'free acid within the sample of the solution will then be boricacid. To prevent dissociation of the alkali borate or borates which are to be formed hereafter, I then add glycerol or mannit to the solution. I then add a few drops of an indicator which' is composed of bromo-cresol purple (dibromo-o-cresol su1- fon phthalein) and bromo-thymol blue (dibromo thymol sulfon phthalein), preferably in the proportions of five parts of the former to one part of the latter. An important feature of my invention is that this indicator will give a distinctive color at the moment when a standard alkali (such as NaOH) has been added in just sufficient quantity (with agitation) to neutralize the acid, converting the boric acid into the appropriate alkali borate. This color-change (which is from green to blue) will occur at a time when this standard alkali .has been added in such quantity that substantially one molecule of such alkali will have beenadded to the sample of solution for each molecule of boric acid contained therein. The color-change referred to will occur when the acidity changes from pH=5 to pH G. The amount ofalkali necessary to be added to bring about this color change will be just sufficient to neutralize the bond acid but will be insutlicient to cause the precipitation of any nickel which may be present in the solution. That i's to say, the indi cator will perform its function of showing the moment when the acid is neutralized, ir-

respective of the presence or absence of or other salts of the alkalis or other nonl. interfering bases and that, in such deter- 1. The method of determining boric acid present in" anickel-containing solution, said method comprising the addition, to a measured volume of said solution, 015 a standard acid in suiiicient quantity to convert any borates that may be present into boric acid; then adding .to the solution an agent capable of preventing the dissociation of the alkali borate or borates Ito beformed thereafter;

kali, with agitatiom until a characteristic then adding to such solution an indicator operative within limits of acidity from pHza to,pH -:6 to impart a characteristic color to thesolution immediately upon the neutralization of the boric acid; and then adding to the solution a standard alkali, with agitation, until such characteristic color, is obtained.

' 2. The method of determining boric acid present in a nickel-containing solution, said method comprising the addition, to a measured volume of said solution, of a standard acid in sufficient quantity to convert any borates that ma I be resent into boric acid; then adding to t e so ution an agent capable of preventing the dissociation of the alkali to be formed thereafter; then addin to such solution an indicator consisting oi bromo- 'cresol purple and bromo-thymol blue; and finally adding to the sglution a standard alcolor is obtained.

3. The method of determining boric acid in a nickel-containing solution which comprises titrating the solution with a standard acid, in the presence of an indicator operative within limits of acidity from pHz5 to pI-I=6, until a characteristic change of color is imparted to such solution; and then'titrating the solution with a standard alkali, in

the presence of glycerol or' mannit and in the presence of an indicator capable of impartin a characteristic color to the solution upon t e neutralization of the acid and irrespective of the presence of nickel or nickel salts in thefsolution.

4. The method of determining boric acid in a nickel-containingsolution which C0111- prises titrating the solution with a standard acid, in thepresence of an indicator,- until a characteristic change of color is imparted to 5 such solution; and then titrating the solution with a standard alkali, in the presence of glycerol or mannit, and wit-h an indicator comprising a mixture. of bromo-cresol purple and bromo-thymol blue.

-5. The process of determining boric acid in a nickel-containing solution which comprises titrating the solution with a standard alkali in the presence of mannit or glycerol and with the employment of an indicator composed of approximately five parts of bromo-cresol purple to one part of bromothymol blue.

6. The process of determining boric acid in a nickel-containing solution which comprises titrating the acidified solution with a standard alkali in the presence of mannit or glycerol and with the employment of an indicator composed of bromo-cresol purple and bromo-thymol blue in proportions to produce a characteristic color-change immediaaely upon the neutralization of the boric aci 7. The process of determining boric acid in a nickel-containin solution which comprises titrating the solution with a standard alkali in the presence of mannit or glycerol and with the employment of an indicator composed of bromo-cresol purple and bromothymol blue in such proportions as will produce a sharp color-change at the time when one molecule of the alkali has been added for each molecule of boric acid present in the solution at the time of beginning the addition of alkali.

8. In the determination of boric acid in a nickel-containing solution, the employment of an indicator operative within limits of acidity from pH:- 5 to pH:6 to giveasharp or characteristic change of color as soon as all of the boric acid has been neutralized or reacted upon by a standard alkali and be fore suiiicien t alkali has been added to react additionally with any nickel salt.

9. In the determination of boric acid in a nickel-containing solution, the employment of bromo-cresol purple and bromo-thymol blue in 'such relatlve proportions as will give a sharp or charactertistic change of coloras soon as all of the boric acid has been neutralized or reacted upon by a standard alkali and before suliicient alkali has been added to react additionally with any nickel salt.

10. The method of determining boric acid in a nickel-containing solution having all of the borate content in the form of boric acid and containing also an excess of other acid or acids, said method comprising titrating the solution with a standard alkali, in the presence of an indicator operative within limits of acidity from pH 5 to pH:6 to impart a charactertistic color to the solution immediately upon the neutralization of the boric acid.

11. A mixture of bromo-cresol purple with bromo-thymol blue in proportions suitable to form an indicator capable of undergoing lution of bromo-thymol blue in substantially a, sharp change in color immediately upon the proportions of five arts of the former neutihlization by a standard alkali of the solution to one part of tie latter solution.

boriaoid in a nickel-containing solution. In testimony whereof, I hereunto aflix my 5 12. An indicator comprising a mixture of signature.

a solution of bromo-cresol purple with a, so- WIN BAKER. 

